On-column epimerization of dihydroartemisinin: An effective analytical approach to overcome the shortcomings of the International Pharmacopoeia monograph

We developed a cryo-HPLC/UV method for the simultaneous determination of artemisinin (1), α-dihydroartemisinin (2α), β-dihydroartemisinin (2β), and a ubiquitous thermal decomposition product of 2 (designated as diketoaldehyde, 3), starting from the International Pharmacopoeia monograph on dihydroartemisinin. The method takes for the first time the on-column epimerization process of 2 into consideration. Chromatographic separation was obtained under reversed-phase conditions on a Symmetry C18 column (3.5 μm particle size) with a mobile phase consisting of acetonitrile–water 60:40 (v/v), delivered at 0.60–1.00 ml/min flow-rates, with ultraviolet detection at low wavelength (λ = 210 nm). Low temperatures (T = 0–10 °C) were selected on the grounds of a diastereoselective dynamic HPLC (DHPLC) study performed at different temperatures, aimed at identifying the best experimental conditions capable of minimizing the on-column interconversion process.